A158864 - OEIS

A158864

Numbers k such that prepending 6 to the k-th triangular number produces a prime.

13, 37, 73, 118, 166, 217, 313, 433, 457, 493, 538, 541, 553, 601, 613, 637, 706, 826, 853, 898, 958, 1042, 1057, 1138, 1222, 1357, 1441, 1513, 1666, 1681, 1777, 1858, 1966, 1993, 2173, 2281, 2341, 2422, 2446, 2518, 2626, 2638, 2653, 2686, 2701, 2737

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Or, concatenated T(3) and T(k) are prime. Or, concatenated A000217(3) and A000217(k) are prime.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

T(13)=91, 691 is prime, so 13 is a term;

T(37)=703, 6703 is prime, so 37 is a term;

T(73)=2701, 62701 is prime, so 73 is a term.

MATHEMATICA